Developing and assessing vegetation indices:
The recently-developed SpecNet index, the Chlorophyll/Carotenoid Index (CCI), offers improved tracking of GPP phenology (relative to NDVI, NIRv).
In evergreens, the strong CCI-GPP relationship is driven by seasonal changes in pigment pool sizes.
CCI also works as a GPP indicator in deciduous and annual vegetation.
Seasonal changes in CCI and pigment pools appear to be closely related to chlorophyll fluorescence (and potentially SIF).
Read more about the CCI: https://www.pnas.org/content/113/46/13087